Method of operating a spark ignition internal combustion engine



3,b5,742 Patented Nov. 27., 1962 3,065,742 METHOD F OPERATING A SPARK HGNITIQN INTERNAL COMBUSTION ENQKNE Fred K. Kawahara, Park Forest, Ill., and Russell H. Brown, Munster, and Charles B. Tracy, Vaiparaiso, Ind, assignors to Standard Gil iloznpany, Chicago, 111., a corporation of Indiana No Drawing. Fiied Feb. 27, 1959, Ser. No. 795,926

Claims. (Cl. 123-1) This invention relates to improvements in the suppression of surface ignition caused by leaded gasolines in the operation of internal combustion engines. More particularly, the invention provides an improved motor fuel for spark ignition internal combustion engines which is effective in suppressing surface ignition or preignition.

Modern automotive engines operating at high efficiencies and high performances are extremely sensitive to proper detonation of the air-fuel mixture in the combustion chamber. Apparently, two distinct phenomena occur, each of which may lead to improper ignition and result in severe power loss. One such phenomenon is the increase in octane requirement of the engine caused by carbonaceous deposits from the fuel and lubricant oil which form on the combustion cylinder walls; by preventing adequate heat removal by the engine coolant and by decreasing the effective cylinder volume, these deposits can be responsible for increasing the octane requirement of a given engine by as much as fifteen octane numbers.

The second efficiency-destroying phenomenon, and one which becomes more serious as engine compression ratios are increased is surface ignition or pre-ignition. Preignition evidently is associated with the use of tetraethyl lead in gasolines. It is generally believed that inorganic compounds of lead catalyze the oxidation of carbonaceous residues on combustion cylinder walls and initiate the glowing of these residues at relatively low temperatures. This glowing ignites the air-fuel mixture before proper spark plug action takes place and causes the phenomenon commonly termed preignition.

Many additives are known which have the ability to reduce preignition. Phosphorous-containing materials, and certain additives which contain both phosphorous and sulfur, have been shown to be effective for this purpose. However, many of these additives give rise to serious problems in engine operation. For example, most com- 'mon preignition suppressants are pro-knocks, and actually decrease the octane number of the fuel. Also, many cause undesirable valve stickiness, are extremely corrosive in storage before use, are insoluble in fuels at low temperatures, and promote oxidative gum formation.

A primary object of this invention is to provide a fuel containing a preignition suppressant additive which imparts to the fuel outstanding resistance to preignition, yet which avoids this usual significant decrease in octane number. Another object is to provide a fuel which eliminates valve functioning difficulties and which is stable and non-corrosive. A further object is to provide an additive concentrate for such fuels which can be employed in imparting preignition suppressant characteristics to motor fuels. Other and more particular objects will become apparent as the description of the invention proceeds in detail hereinafter.

In accordance with the invention a motor fuel is provided for spark ignition internal combustion engines containing a minor amount of tetraethyl lead and, in an amount sufficient to give a mol ratio of phosphorous to lead in the range of from about 0.01 to about 1.0, the reaction product of a phosphorous sulfide and an olefinic hydrocarbon, which reaction product has been esterified with an alkanol having from one to twelve carbon atoms per molecule. The phosphorous sulfide is preferably phosphorous pentasulfide and the olefinic hydrocarbon may be an olefin having from two to forty carbon atoms per molecule, preferably from four to twenty carbon atoms. The alkanol employed for esterification, although it may be any primary, secondary or tertiary alcohol, and can contain from about one to about twelve or more carbon atoms per molecule, preferably is a primary alcohol containing from three to eight carbon atoms per molecule. Although all combinations of olefinic hydrocarbons and alkanols appear to give excellent preignition suppression, at particular advantage of the inventive additives is that they may be prepared from very low molecular weight materials, and thus can be used at all effective concentrations and at all temperatures without incurring solubility difficulties and without causing the valve stickiness associated with higher molecular weight additives. Examples of alkanols useful in accordance herewith include methanol, ethanol, isopropanol, n-butanol, n-amyl alcohol, n-octyl alcohol, 2-ethyl hexanol, n-decyl alcohol, etc. With alcohols having more than about twelve carbon atoms, an undesirable tendency toward engine valve stickiness is exhibited.

The motor fuels to which are added the inventive additives are hydrocarbons of the gasoline boiling range, i.e. boiling within the range of from about F. to about 500 F., and preferably in the range of about F. to about 400 F. The gasolines may be hydrocarbons of any type, including normal paraflins, isoparafiins, olefins, and naphthenic and aromatic hydrocarbons of any octane number, and may be derived in whole or in part from crude oil distillation, catalytic cracking of gas oils, catalytic reforming of naphthas, polymerization of low molecular weight olefins, alkylation of isoparafiins with olefins, etc. Such motor fuels contain tetraethyl lead in a concentration of from about 0.5 to about 5 cubic centimeters (co) per gallon of fuel; typically tetraethyl lead is introduced as ethyl fluid containing about equal amounts of tetraethyl lead and ethylene dibromide and/or dichloride as a halogen scavenger. Motor fuels may also contain anti-oxidants, copper deactivators, stabilizers, dyes, anti-icing agents, and/or other compounds normally employed in leaded motor fuels.

In preparing the phosphorous-sulfide olefin reaction products, an oiefinic hydrocarbon is reacted with a phosphorous sulfide with a P 8 P 8 P 8 or other phosphorous sulfides, and preferably pentasuifide, P 8 at a suitable temperature within the range of about 150 F. to about 600 F. The reaction between phosphorous sultide and olefinic hydrocarbon consumes one mole of olefin per gram atom of phosphorus, although an excess of either reactant may be present.

The olefinic hydrocarbon component used in preparing the reaction product is preferably a monooiefinic alkene or cycloalkene having from two to about forty atoms per molecule, more desirably from four to twenty carbon atoms per molecule. Such olefins as l-butene, isobutylene, l-pentene, Z-pentene, l-hexene, l-heptene, l-octene, l-nonene, l-decene, cyclohexene, methylcyclopentene, either individually or in admixture with each other, may be used. An especially favored type of olefinic hydrocarbon reactant are the olefin polymers which are prepared by catalytically polymerizing under known conditions a normally gaseous olefin such as propylene, isobutylene, l-butene or Z-butene. The polymerization of propylene using, for example, phosphoric acid-on-kieselguhr is common in the petroleum refining industry. The resultant polymer may be fractionated to furnish, for example, propylene dimer, propylene trimer, butylene dimers, propylene tetramer, et-o. Propylene trimer is an 3 exceptionally useful and low cost hydrocarbon reactant for use herein.

In general, the preparation of the phosphorous sulfideolefinic reaction product in accordance with the present invention is carried out in the following manner:

The hydrocarbon, such as, for example, an olefinic polymer of the desired carbon chain length is reacted with about 1% to 50%, based on total reaction mixture, and preferably from about 10 to 25% of a phosphorous sulfide, e.g. P S at a temperature of from about 150 F. to about 600 F., preferably 230 F. to 450 F., in a non-oxidizing atmosphere, such as, for example, an atmosphere of nitrogen. The reaction is carried out for from about one to about ten hours or more, and preferably for about five hours. The phosphorous-sulfide hydrocarbon reaction can, if desired, be carried out in the presence of a sulfurizing agent such as elemental sulfur or a halide of sulfur.

The reaction product of phosphorous sulfide and an olefinic hydrocarbon is then esterified with the hereinbefore described alkanol. The esterification step may be carried out catalytically or non-catalytically at any convenient temperature up to the decomposition temperature of the reactants or products, although it is preferred to carry out the reaction at a temperature between about 100 F. and about 400 F. and for a period of time ranging from two to about twenty hours in a non-oxidizing atmosphere, using a molar excess (-10 mols excess) of alkanol. At the conclusion of reaction, excess alkanol can be removed from the inventive additive and recovered by mild heating under vacuum, although the presence of certain alkanols in gasoline is often desirable as an anti-icing agent.

As specific illustrative embodiments of our invention, the following examples are given. It is to be understood that these are by way of illustration only and are not intended as a limitation of our invention:

EXAMPLE 1 In this example, the reaction product of propylene trimer with phosphorous pentasulfide was prepared and then esterified with n-butanol. Phosphorous pentasulfide, 444 parts by weight, was added gradually to 504 parts of propylene trimer at 200 F. The mixture was brought to 280 F. and held at that temperature for four hours in a nitrogen atmosphere, after which the resultant reaction product was cooled and then filtered at 180 F. through celite. To 73 parts of propylene trimer-phosphorous pentasulfide reaction product was added a large molar excess of n-butanol, 219 parts in all of alcohol. This mixture was then heated at 240 F. for eight hours in a nitrogen atmosphere. Excess alcohol was removed under vacuum. The resultant additive was completely soluble in hexane and in aromatic solvents. Analysis: phosphorous 11.05%; sulfur 21.2%.

This additive product will be hereinafter termed propylene trimer-P s -n-butanol.

EXAMPLE 2 In this example, an additive was prepared by esterifying with n-butanol the reaction product of phosphorous pentasulfide and l-heptene.

The procedure essentially followed that employed in Example 1 above. The reaction product was prepared from 111 parts by weight of phosphorous pentasulfide and 118 parts by weight of l-heptene in 83 parts of SW base oil; and 314 parts by weight of the reaction product was reacted with 152 parts of n-butanol. The additive product analyzed 5.22% phosphorous and 12.1% sulfur.

In subsequent discussions, the additive product is termed heptene? S -n-butanol.

To test the inventive additives as preignition suppressants and to compare them for this purpose with well known preignition suppressants, engine tests were made using a single cylinder CPR-L head engine having a 7:1 compression ratio. Typical operating conditions for preignition studies are as follows:

4: Test duration hours 50 Coolant temperature F 148 Oil temperature F 160 Air to fuel ratio 13/ 1 For this test the engine is cycled as follows:

Cycle Conditions Surface ignition prevention effectiveness was determined using a fuel containing 3 cc. of TEL per gallon and containing various preignition suppressant additives. The additives used were (1) propylene trimer-P S -n-butanol prepared in Example 1, (2) commercially available tricresylphosphate or TCP, and (3) commercially available Xylyl dimethyl phosphate or XDP. All additives were used in a concentration sufficient to provide a mol ratio of phosphorous to lead (M.R.P/ Pb) of 0.13.

The following results were obtained on the CPR-L engine:

Additive: Effectiveness Propylene trimer-P S -n-butanol percent 83 XDP do 54 TCP do 50 Thus the above table demonstrates that the present additives are substantially superior to similar additives currently on the market.

It was previously indicated that one of the major disabilities of preignition suppressant additives is their adverse effect on the octane rating of fuels. Although this appears at present to be an insurmountable problem, tests were made to demonstrate that the inventive additives are more satisfactory in this respect than competitive and heretofore available materials. This test was run using a CPR-L head engine fueled with a premium gasoline of 93-94 octane number containing 3 cc. of TEL per gallon and 0.3 wt. percent of SAE30 base oil. The antiknock depreciation, in terms of octane number decrease of the fuel, caused by the inventive additives and by equivalent concentrations of other additives are shown in the table below.

The inventive additives also possess the unusual property of extending spark plug life in automobile engines. In a series of tests using an Oldsmobile engine, the spark plug life was 117 hours with a motor fuel containing 3.0 cc. TEL per gallon and no additive, but the life was increased to 139 hours when the engine was fueled with the same fuel containing 0.13 M.R. P/Pb of heptene-P S -n butanol. In another test, using the Oldsmobile engine, a fuel containing 0.13 M.R. P/Pb of heptene-P s -n-butanol increased spark plug life from 112 to 128 hours.

One of the major problems with preexisting phosphorous sulfide-hydrocarbon reaction products is insolubility in gasoline at suitably effective concentration levels. To evaluate the present additives, the gasoline solubility test was employed using an additive concentration of 0.13 M.R. P/Pb concentration level. The test involved adding 0.13 M.R. P/Pb of phosphorous compound to 25 ml. of gasoline and observing the solubility.

. Additive:

Propylene dimer-P 8 n-butanol Soluble. Heptene-P S -n-butanol Soluble. Proplylene t-ri1ner-P S steam hydrolyzed Dissolves temporarily, then precipitates out.

Solubility io evaluate the various additives for their tendency to avoid fuel system clogging, the modified Chevrolet Induction System Deposit (131)) test was employed. The fuel consisted of leaded premium grade gasoline containing 0.13 MR. P/Pb additive. This test is run on a 1953 Chevrolet engine having 216 cubic inch displacement operated under the following conditions for 40 hours:

At the end of the 40 hours, the engine is dismantled and the induction system and intake and exhaust valves examined. The additive prepared in Example 1 rated pass, with only one intake valve slightly fouled.

To demonstrate under strictly comparable conditions the superiority of the inventive additives overrelated prior-art materials with respect to induction system deposit-forming tendencies, the slide valve test was employed. This consists in passing a lead gasoline contain ing 3 cc. of TEL per gallon and 0.13 MR. P/Pb of additive through a weighed open trough 18 inches long and positioned at a 15 angle, the trough being maintained at 400 F. At the end of the test, the trough is washed once with hexane and once with a mixture of alcohol, acetone, and chloroform. The Weight of residual deposits is taken as the slide valve rating of the additive; a rating of 15 mg. of deposit is considered to be acceptable.

The following results were obtained in the slide valve test:

Additive: Slide valve Propylene trimer-P S -n-butanol Il'lE' Heptene-P S -n-butanol mg 17.1 Propylene dimer-P 5 steam hydrolyzed mg 74.9 Propylene trin1er-P S product mg 72.4

The above results clearly demonstrate that the inventive additives are uniquely able to virtually eliminate undesirable gum formation in the induction area.

Another problem frequently associated with the use of preignition suppressants is the considerable reduction of oxidation stability of the fuel in storage, as measured under the conditions of the ASTM induction period test. A series of tests was therefore run, the results of which are shown below, to establish the effect of various concentrations of propylene trimer P S -n-butanol on the induction period. The following test results were observed, and show that the effect on induction period is inconsequential.

A large number of otherwise satisfactory preignition suppressants are entirely useless as motor fuel additives since they accelerate copper strip corrosivity under the o conditions of the ASTM copper strip test. Using a leaded premium gasoline and concentrations of 0.13 and 0.33 MR. P/Pb of propylene trimer P S -n-butanol, copper strip tests run at 122 F. showed absolutely no change over the additive-free gasoline.

The percentages given herein and in the appended claims are weight percentages unless otherwise noted.

We claim:

1. A hydrocarbon motor fuel of the gasoline boiling range suitable for spark ignition internal combustion engines, containing a minor amount of tetraethyl lead and, in combination therewith, in an amount sufficient to provide a mol ratio of phosphorous to lead in the range of from about 0.01 to about 1.0, the reaction product of a phosphorous sulfide and a hydrocarbon, which has been esterified with an alkanol having from one to twelve carbon atoms per molecule, said reaction product having been prepared by reacting one gram atom of a phosphorous sulfide with one mole of an olefinic hydrocarbon having from two to about forty carbon atoms per molecule, inclusive, at a reaction temperature of from about F. to about 600 F.

2. The motor fuel of claim 1 wherein said tetraethyl lead is present in the range of from about 0.5 to 5.0 cubic centimeters per gallon of said fuel.

3. The motor fuel of claim 1 wherein said alkanol has from three to eight carbon atoms per molecule.

4-.'T he motor fuel of claim 3 wherein said alkanol is n-butanol.

5. The motor fuel of claim 1 wherein said phosphorous sulfide is phosphorous pentasulfide.

6. The motor fuel of claim 1 wherein said olefinic hydrocarbon has from four to twenty carbon atoms per molecule, inclusive.

7. A hydrocarbon motor fuel of the gasoline boiling range suitable for spark ignition internal combustion engines, comprising a major amount of a hydrocarbon mixture boiling in the gasoline distillation range, from about 0.5 to 5 .0 cubic centimeters of tetraethyl lead per gallon of said fuel, and, in an amount sufiicient to give a mol ratio of phosphorous to lead in the range of from about 0.1 to about 1.0, the reaction product of phosphorous pentasulfide and an olefinic hydrocarbon which has been esterifiecl with an alkanol having from three to eight carbon atoms per molecule, said reaction product having been prepared by reacting one gram atom of phosphorous pentasulfide with one mole of an olefinic hydrocarbon having from two to about forty carbon atoms per molecule, at a reaction temperature of from about 150 F. to about 600 F.

8. An additive concentrate for gasoline which consists essentially of tetraethyl lead and, in an amount sufficient to give a mol ratio of phosphorous to lead of from about 0.1 to about 1.0, the reaction product of a phosphorous sulfide and an olefinic hydrocarbon which has been esteritied with an alkanol having from one to twelve carbon atoms per molecule, said reaction product having been prepared by reacting one gram atom of a phosphorous sulfide with one mole of an olefinic hydrocarbon having from two to forty carbon atoms per molecule, inclusive, at a reaction temperature of from about 150 F. to about 600 F.

9. The additive of claim 7 wherein said alkanol has from three to eight carbon atoms per molecule, said phosphorous sulfide is phosphorous pentasulfide, and said olefinic hydrocarbon has from four to twenty carbon atoms per molecule.

10. The method of operating a spark ignition internal combustion engine which comprises supplying to said engine a gasoline composition comprising a major amount of a hydrocarbon fuel boiling in the gasoline boiling range, from about 0.5 to 5.0 cc. of tetraethyl lead per gallon of said fuel, and, in an amount sufiicient to give a mol ratio of phosphorous to lead in the range of from about 0.01 to about 1.0, the reaction product of a phosphorous References Cited in the file of this patent UNITED STATES PATENTS Hill et al July 5, 1955 Bartleson June 4, 1957 Bartleson June 4, 1957 Bartleson May 3, 1960 

